Historically in the United States authorities such as city, state, or federal police authorities, may engage in electronic surveillance (frequently referred to in the vernacular as wire-tapping), when duly authorized to perform such an activity by a cognizant judicial authority. In earlier times, when public telephone service was virtually all analog the procedure was relatively simple. Assuming surveillance of a residence connected to the telephone network by a local loop consisting of a pair of copper wires, the usual practice was to locate a convenient cross connect and bridge on to the two wire analog circuit. The entity conducting the surveillance then engaged the serving telephone network operator or company to provide a circuit from that location to the law enforcement location. The law enforcement organization could then monitor the conversations, generally referred to as content, as well as the call set up and related signaling. Statistically approximately 90 percent of the authorized surveillance in the United States does not cover content but signaling data. Such events are referred to as Pen register taps.
With the widespread use of digital communication and control signaling, the simplicity and ease of the prior surveillance procedures has largely disappeared. As a result, law enforcement agencies, and cooperating Public Switched Telephone Networks (PSTNs), are forced to cope with a considerably more complex and costly substitute set of procedures. Partially in response to this situation Congress passed Public Law 103-414, the Communications Assistance for Law Enforcement Act (CALEA). The Telecommunications Industry Association (TIA), accredited by the American National Standards Institute (ANSI), was selected by the telecommunications industry to promulgate the industry's CALEA standard. TIA promptly initiated a standards program. Initial disagreements within industry were resolved, and TR45 Lawfully Authorized Electronic Surveillance SP-3580, Baseline Revision 10 was produced. These have become known as the "safe harbor" standards pending resolution of still outstanding differences with respect to certain preferences of the Federal Bureau of Investigation (FBI).
The CALEA specifications include the requisite that the target for surveillance continue to be provided with all subscribed enhanced, CLASS, and other services, and that the surveillance be completely transparent. The central office switches currently in use in the public switched telephone networks were not designed with CALEA functionalities in mind. As a result it is not surprising that not all types of existing switches are readily adapted to operate in a network that meets major CALEA requirements.
The basic surveillance problem has undergone continued evolution as telecommunications technology has advanced and provided the public with an ever-increasing variety of services. Illustrative of such services, which create added complexity for effective telephone surveillance, is call forwarding and particularly remotely activated call forwarding. Another example is central office based speed dialing.
Since the proposed CALEA requirements are worded in terms of service, i.e., monitoring the telephone service (signaling and speech) of the subject, and anything that can be accomplished with the service, significant problems are presented. This becomes particularly acute when coupled with a desire that the surveillance preferably be near universally applicable to all telephone central offices, including end offices that rely on legacy switches. One example of a specific problem is encountered with end offices using Lucent (formerly AT&T) 1AESS switches. These switches are among the earlier variety of stored program controlled switches and are rapidly being retired. As a consequence, it would not be wise to expend large sums to develop CALEA feature software for these switches. On the other hand the later Lucent 5ESS switches will be in service for many years to come and it may make sense to develop the requested surveillance capabilities in a number of network configurations. Cost considerations weigh heavily in selecting and providing an acceptable solution.
It is accordingly an object of the present invention to provide a relatively straightforward and cost effective solution to the foregoing problem.